StarChild Question of the Month for December 1998

Question:

Is there a Planet X or 10th planet?

Answer:

There is no known Planet X or 10th planet in our solar system.
Scientists have been looking for about a hundred years. It was believed that
such a planet was required to explain the orbital characteristics of the
outer planets Uranus and Neptune. Many searches have been performed and,
to date, no evidence of such a planet has emerged. In addition, better
information about the masses of outer planets has also now shown
that no other planets are necessary to explain the planetary orbits.
You can get a good historical
account of the searches for "Planet X" at:
http://nineplanets.org/hypo.html#planetx

Yet, there are new planets being discovered!However,
any new planets you may hear, or have heard, about being discovered are around
other stars, not our Sun! You can read all about the search for, and discovery
of, planets around other stars at
http://nineplanets.org/other.html
or get a very comprehensive discussion at
http://www.public.asu.edu/~sciref/exoplnt.htm#preface

How will these new planets be named? The planets that are being found around
other stars are given scientific
catalog names (like SV168) and not the names of people (real or
mythological). All objects, whether moons or asteroids or planets, are
named by the International Astronomical Union according to strict
guidelines. You can read about this at
http://www.iau.org/MINOR_PLANETS_NAMING.245.0.html